I have a Medis rangefinder and yes it can be way out over the full range of distances depending on how you set it up. For instance mine goes from 20ft to infinity almost immediately(if set up 'by the book'), a massive jump. Some rangefinders are better, Voigtlander, or Wattameter in my experience. But if you set the rangfinder up so it is accurate in the near to middle distance then the rest should be common sense if it starts to look fishy at longer distances, and DOF will often cover the inaccuracy.
I have a Widor with adjustable horizontal and vertical alignment, and it's accurate at all distances. For the close distance, I set the rangefinder and the lens at 3 feet and move my head back and forth while looking through the rangefinder until it's in focus.
I have an accessory Voiglander rangefinder that lives with my father's old Vito B. They are both scaled in feet. It comes in handy between say 15 and 3 feet where DoF won't save you.